This invention relates to an electric field forming apparatus for use in a fryer for frying food. More particularly, it relates to an electric field forming apparatus for a fryer which applies a high voltage to an electrode disposed in an oil vat and generates an electric field in the oil vat. It also relates to a fryer which utilizes this electric field forming apparatus and to a method of frying food.
As described in Japanese Published Unexamined Patent Application 2001-95695, it has been proposed to dispose a flat electrode at the bottom of an oil vat of a fryer and to apply a high voltage to the electrode to form an electric field within the oil vat. Forming an electric field in an oil vat is said to provide benefits such as suppressing oxidation of oil in the vat, preventing contamination, and shortening the frying time. These benefits are thought to be primarily due to the electric field producing forced convention of oil in the oil vat, which promotes the transmission of heat to food and produces concentrated heating of the surface of the food. This results in rapid frying of the surface of the food and trapping of moisture within the food. Since moisture is prevented from flowing into the oil, an oxidation reaction between oxygen in the moisture and oil is prevented. It has also been proposed to detachably install a flat electrode parallel to a side wall of an oil vat (see Japanese Published Unexamined Patent Application No. 2004-41531).
However, the electric field forming apparatus described in Japanese Published Unexamined Patent Application 2001-95695 has a structure such that the bottom portion of an oil vat of a fryer is electrically charged by an electrode which extends over the entire bottom surface of the oil vat, so food which is placed into the oil vat adheres to the bottom inner surface of the oil vat. Convection of oil is insufficient in locations where adhesion of food takes place, so the effect of promoting uniform heat transmission by the electric field cannot be obtained. In particular, heating of the surface of food facing the bottom surface of the oil vat is delayed, and unfried portions end up forming in the food. In the electric field forming apparatus described in Japanese Published Unexamined Patent Application 2004-41531, a flat electrode is disposed parallel to a side wall of an oil vat, so the problem of adhesion of food to the bottom of the oil vat is avoided, but since the electrode extends along a vertical surface of the oil vat, the efficiency of the electrode is poor, and adequate heat convection to the underside of food cannot be produced. Namely, in order to obtain a uniform fried state, it is important to generate a strong electric field in the vicinity of the bottom of the oil vat, but with the electric field forming apparatus described in Japanese Published Unexamined Patent Application 2004-41531, the electrode spreads in the vertical direction along a side wall of the oil vat, so an electric field cannot be concentrated at the bottom portion of the oil vat, and the electric field which is generated cannot be effectively utilized. Therefore, the desired effect of applying an electric field to oil in an oil vat cannot be adequately obtained.